The present invention relates to coated thermoplastic polymer compositions and methods of making and using such compositions. The coating comprises at least one mineral, and clays in particular. The coating renders the thermoplastic polymer less permeable to gases, such as oxygen and carbon dioxide.
Thermoplastic polymer and related resins are often used as materials for food and beverage containers, particularly for carbonated beverages such as soda and beer. The advantages to using xe2x80x9cplasticxe2x80x9d bottles are numerous, and include lighter weight, lower cost, recyclability and increased safety to the consumer. However, there are some disadvantages, including their inherent permeability to gases. Because thermoplastic polymer materials, such as poly(ethylene terephthalate) (PET), are permeable with respect to gases such as oxygen and carbon dioxide, the contained beverages have a relatively short shelf-life, i.e., either go xe2x80x9cflatxe2x80x9d as carbon dioxide permeates out or xe2x80x9cspoilxe2x80x9d as oxygen permeates into the beverage.
Decreasing the permeability of the container material is desired, and several options have been explored. These include coating the outside of the containers with a solid film of less-permeable material, which can provide added expense and weight, and which can fail if the film lacks adhesion to the container. Another way has been to provide a coating to the inside of the container, but this coating must be approved by the FDA as permissible for food contact. Still another way has been to include a component within the resin itself (e.g., an exfoliated clay or mineral) to improve the permeation resistance, but often the ease of polymer processing and the mechanical properties are sacrificed. Since the clay is dispersed within the resin, a higher loading of clay is required to achieve the same permeation resistance than if the clay were concentrated along an interface.
EP 0 778 153 A1 discloses a laminated film comprising a base film and a layer which contains an inorganic layered compound and a resin. The film is produced by gravure coating. Examples of resins for the base film are polyolefin resins, polyester resins, amide resins, acrylic resin, hydrophobicized cellulose resins, hydrogen-bondable resins, and engineering plastics. Since the layered compounds are dispersed within the resin, the layered compounds are not bound directly to the base film, and a higher loading of clay is required to achieve the same permeation resistance than if the clay were concentrated along an interface of the film base. Furthermore, the resin component of the coating adds to the total cost of the fabricated item.
The present invention relates to a composition comprising a thermoplastic polymeric substrate, and a coating consisting essentially of a layered mineral.
The present invention also relates to a method of making a composition comprising a thermoplastic polymeric substrate and a coating consisting essentially of a layered mineral, comprising the step of contacting a substrate comprising a thermoplastic polymer having pendant groups receptive to a layered mineral with a solution consisting essentially of a layered mineral and a dispersant.
The present invention further relates to a method of reducing the gas permeability of a thermoplastic polymeric substrate comprising applying a coating consisting essentially of a layered mineral to a thermoplastic polymeric substrate having at least one surface functionalized with pendant groups receptive to the layered mineral.
The present invention also relates to a method for packaging a liquid in a molded biaxially oriented polymeric container comprising the steps of forming a container; applying a coating consisting essentially of a layered mineral to at least one surface of said container; introducing a liquid into the container; and sealing the container.